The present invention provides a process for smooth cut printing.
The usual processes for smooth cut printing of documents consist in using a thin plate, a shell, a collar or a cylinder, all of them called plate in the following description, preferably made of metal wherein the pattern to be reproduced through printing is sunk engraved. Some areas of said plate are coated with ink so that the ink penetrates the hollows or cuts of same. The inked surface is wiped out in order to leave ink in the hollows only and the surface thus inked and wiped out is applied against an appropriate support, such as a sheet or a strip of paper, by means of a pressing cylinder; thus, a part of the ink is transferred from the hollows onto the sheet.
According to some processes, an indirect transfer of the ink contained in the hollows of the plate is performed by means of a cylinder carrying a flexible coating and positioned between the plate and the support.
In the known processes, the wiping operation causes a great loss of ink. As a matter of fact, the coating of the engraved plate with ink is performed at 100%, and the wiping thereof removes, depending on the case, about 75% of said ink; this corresponds to the parts of the area which do not carry any cut and do not serve for printing. Said 75% of wiped ink constitute wastes. Where a printing with several colors is involved by using one and the same plate each zone of which receives inks of different colors, the waste problems remain. Furthermore, in view of the wiping, the risk is run of running one color into another one and also of mixing colors which spoils the quality of the print.
A process and a machine for smooth cut printing is already known and disclosed in French Pat. No. 1,564,653.
Said process consists in coating the plate before inking it, with a colorless liquid, non-miscible with ink, then in applying the ink. Generally, the non-miscible liquid is filtered water.
Such an improvement to standard processes is aimed to minimise the losses of ink and to increase the sharpness of the printed patterns, as well as to prevent or simplify the wiping operation.
Unfortunately, the practice has shown that this process which rests on a physical balance between the water and ink is suitable only for a given depth of the cut and not for all depths of smooth cuts with various depths as most of them. This greatly limits the scope of the process and practically prevents its use.